U.S. Pat. No. 3,704,287 describes polymerization catalysts formed by activating a chromate ester-supported on a carrier with an aluminum, magnesium or gallium organometallic compound. Prior to U.S. Pat. No. 3,704,287, U.S. Pat. Nos. 2,825,721 and 2,951,816 showed the use of chromium oxide, containing some hexavalent chromium, (at least in the early stages of polymerization) on a carrier to catalyze the polymerizations of 1-alkenes; in those systems, catalytic activity was optimized by heating the catalyst in a non-reducing, preferably oxidizing, atmosphere. U.S. Pat. No. 2,824,089 and Canadian Pat. No. 624,913 and teach polymerizing 1-alkenes in the presence of a catalyst consisting of a supported oxide of a metal of Group VI.sup.b of the periodic system, e.g. chromium oxide, and an organometal compound of an element of Group III of the Periodic System, e.g. boron or aluminum. Further, combinations of chromium compounds with compounds of other elements have been employed, for instance, phosphorus oxides as reflected by Canadian Pat. No. 619,801 or catalysts based on a chromium compound not being an oxide as reflected by U.K. Pat. No. 1430463 and German Offenlegungsschrift No. 2,307,147, which describe use of catalysts produced by activating chromium (III) acetyl acetonate supported on silica with an aluminum trialkyl.
It is an object of the invention to provide a process for the polymerization of 1-alkenes in the presence of a supported chromium compound serving as an active catalyst which gives very high yields of a polymer which contains only very minor quantities of catalyst residues.
It is a further object of the invention to provide a process for the polymerization of ethylene. Another object of the invention is to provide a process for the preparation of polyethylene possessing good mechanical and physical properties by polymerizing ethylene containing minor quantities of less than 5 mole% of propylene and/or butylene.